This invention relates to controls for turbine type power plants and more particularly to means for synthesizing a failed sensor to avoid engine shutdown or damage.
The apparent consequence of a failed sensor in the engine control is failure or shutdown of the engine. Obviously, such a consequence is to be avoided if at all possible. Attempts have been made to account for failed sensors particularly as a result of the advent of digital computers. For example, U.S. Pat. No. 3,851,157 granted to S. H. Ellis on Nov. 26, 1974, and assigned to the same assignee, discloses a system that continuously performs mathematical calculations and applies a statistical analysis of sorts to ascertain the probability of sensor failure and means that would substitute for the failed sensor. Such a system is not only complex but is cumbersome to implement and at best it's a statistical approach to the correct answer.
We have found that we can increase failure tolerance of electronic controls by synthesizing burner pressure from the sensed engine and aircraft parameters upon failure of the actual burner pressure sensing system. This invention contemplates generating a calculated compressor inlet total pressure signal (P.sub.T.sbsb.2) from aircraft Mach No. and altitude and multiplying it by the ratio of burner pressure to compressor inlet total pressure (P.sub.B /P.sub.T.sbsb.2) generated from sensed compressor inlet total temperature (T.sub.T.sbsb.2) and sensed rotor speed (N.sub.1) to synthesize burner pressure (P.sub.B).